[Epic] Tiptap integration

[kulmann]

Pull request #2195 introduces a tiptap editor integration, which replaces the markdown editor we had before. It's a small set of editor components which is based on tiptap and offers support for content types plain-text, markdown, html and tiptap-json. The toolbar is content-type-sensitive. The editor offers slash command actions.

On top of the basic integration we to harden the integration by offering a really useful feature set via the sub issues linked in this epic.

Sub-issues:

• Insert and edit Links
• Render inline base64 encoded images
• Upload and inline images base64 encoded
• add menu parent menu for alignment (left, right, center, block) to formatting section in toolbar
• toggle raw source view mode
• toggle line numbers (default off, available both in rendered and raw source view mode)
• drag to move blocks
• + on hover for slash command menu
• new actions for toolbar:
  • export as PDF
  • import from Word
  • text-alignment (only for html and tiptap-json)
• toolbar: inline font size controls
• toolbar: render colors in color dropdowns (background and text color)
• create table by specifying the amount of rows & columns directly at the start via a grid

tbd

• toolbar: inline "turn into" controls (h1, h2, h3, text, code, quote, etc)

[db-ot]

related to https://github.com/opencloud-eu/internal/issues/113

[lukas-scm]

I already created a web app integration with tiptap, maybe it can be used for further development: opencloud-markdown-editor.